1. Field of the Invention
The invention relates generally to the field of drill pipe used in the drilling of wellbores through subsurface rock formations. More specifically, the invention relates to connectors for segments of such pipe that do not require threads.
2. Background Art
The exploration for and production of hydrocarbons from subsurface rock formations ultimately requires a method to reach and extract the hydrocarbons from the formations. The reaching and extracting are typically performed by drilling a wellbore from the Earth's surface to the hydrocarbon-bearing Earth formations using a drilling rig. In its simplest form, a drilling rig is used to support a drill bit mounted on the end of a drill string. The drill string is typically formed from lengths of drill pipe or similar tubular segments connected end to end. The drill string is supported by the drilling rig structure at the Earth's surface. A drilling fluid made up of a base fluid, typically water or oil, and various additives, is pumped down a central opening in the drill string. The fluid exits the drill string through openings called “jets” in the body of the rotating drill bit. The drilling fluid then circulates back up an annular space formed between the borehole wall and the drill string, carrying the cuttings from the drill bit so as to clean the borehole. The drilling fluid is also formulated such that the hydrostatic pressure applied by the drilling fluid is greater than surrounding formation fluid pressure, thereby preventing formation fluids from entering into the borehole.
The fact that the drilling fluid hydrostatic pressure typically exceeds the formation fluid pressure also results in the fluid entering into the formation pores, or “invading” the formation. To reduce the amount of drilling fluid lost through such invasion, some of the additives in the drilling fluid adhere to the borehole wall at permeable formations thus forming a relatively impermeable “mud cake” on the formation walls. This mud cake substantially stops continued invasion, which helps to preserve and protect the formation prior to the setting of protective pipe or casing in the borehole as part of the drilling process, as will be discussed further below. The formulation of the drilling fluid to exert hydrostatic pressure in excess of formation pressure is commonly referred to as “overbalanced drilling.”
The drilling fluid ultimately returns to the surface, where it is transferred into a mud treating system, generally including components such as a shaker table to remove solids from the drilling fluid, a degasser to remove dissolved gases from the drilling fluid, a storage tank or “mud pit” and a manual or automatic means for addition of various chemicals or additives to the fluid treated by the foregoing components. The clean, treated drilling fluid flow is typically measured to determine fluid losses to the formation as a result of the previously described fluid invasion. The returned solids and fluid (prior to treatment) may be studied to determine various rock formation characteristics used in drilling operations. Once the fluid has been treated in the mud pit, it is then pumped out of the mud pit and is pumped into the top of the drill string again.
As the wellbore is made progressively deeper, additional lengths (“joints”) of pipe are added to the drill string. The most common technique for adding such addition joints is to threadedly couple them end to end. The threads transmit axial and torque loading between pipe joints and form a seal to prevent loss of fluid (mud) under pressure as it is pumped through the drill string.
A limitation to the use of threaded connections is that they must be connected so as to avoid cross threading. Threaded connections must be screwed together to a precise torque to prevent damage and to fully transmit rotational energy along the drill string. Threaded connections are also subject to being unscrewed (broken) in the event of “stick slip” motion of the drill string. See, e.g., U.S. Pat. No. 7,140,452 issued to Hutchinson. Further, it is impractical to rotate a drill string in a direction opposed to the threaded connection “make up” direction because of the risk of unscrewing one or more pipe connections.
Accordingly, there exists a need for a type of drill string pipe connection that does not require threads and can be rotated in either direction.